Fix MSVC compiler and linker errors

- Fix struct/class forward declaration mismatches (JAIAudience, JASTrack) causing different MSVC mangled names and unresolved symbols
- Add jsystem_stubs.cpp with stubs for JASHeap, JASVoiceBank, J3DShapeTable, JAUSection, JHICommBuf, HIO/HIO2, JOR

src/d/actor/d_a_obj_wdStick.cpp

@@ -435,7 +435,7 @@ void daWdStick_c::mode_proc_roll() {
     bgCheck();
 }
 
-f32 dummyLiteral() { return 100.0f; }
+static f32 dummyLiteral() { return 100.0f; }
 
 BOOL daWdStick_c::chkWaterLineIn() {
     return mAcch.m_wtr.GetHeight() > current.pos.y + 40.0f;